Uses
Samarium occurs as silver-coloured solid/foils or grey powder and is an odourless, flammable, and water-reactive solid. All forms of samarium are known to react with dilute acids emitting flammable/explosive hydrogen gas. Samarium on contact with water reacts and liberates extremely flammable gases. Samarium is incompatible with strong acids, strong oxidising agents, and halogens. The major commercial application of samarium is in samarium–cobalt magnets. These magnets possess permanent magnetisation property. Samarium compounds have been shown to withstand significantly higher temperatures, above 700°C, without losing their magnetic properties. The radioactive isotope samarium-153 is the major component of the drug samarium 153Sm lexidronam (Quadramet). These are used in the treatment of cancers of lung, prostate, and breast and osteosarcoma. Samarium is also used in the catalysis of chemical reactions, radioactive dating, and in x-ray laser. Samarium is used as a catalyst in certain organic reactions: Samarium iodide (SmI2) is used by organic research chemists to make synthetic versions of natural products.
Samarium occurs with concentration up to 2.8% in several minerals including cerite, gadolinite, samarskite, monazite, and bastnäsite, the last two being the most common commercial sources of the element. These minerals are mostly found in China, the United States, Brazil, India, Sri Lanka, and Australia; China is by far the world leader in samarium mining and production. Radioactive isotope samarium-153 is the major component of the drug samarium (153Sm) lexidronam (Quadramet), which kills cancer cells in the treatment of lung cancer, prostate cancer, breast cancer, and osteosarcoma. The isotope, samarium-149, is a strong neutron absorber and is therefore added to the control rods of nuclear reactors. Samaria oxide is used for making special infrared-adsorbing glass and cores of carbon arc-lamp oxide electrodes and as a catalyst for the dehydration and dehydrogenation of ethanol. Its compound with cobalt (SmCo5) is used in making a new permanent magnet material. Samarium has no biological role, but it has been noted to stimulate metabolism. Soluble samarium salts are mildly toxic by ingestion, and there are health hazards associated with these because exposure to samarium causes skin and eye irritation. One of the most important applications of samarium is in samarium–cobalt magnets, which have a nominal composition of SmCo5 or Sm2Co17. They have high permanent magnetisation, which is about 10,000 times that of iron and is second only to that of neodymium magnets.
Chemical Properties
silvery grey powder
Physical properties
Samarium is a hard, brittle, silver-white metal. When freshly cut, it does not tarnish significantlyunder normal room temperature conditions. Four of its isotopes are radioactive andemit alpha particles (helium nuclei). They are Sm-146, Sm-147, Sm-148, and Sm-149.
Its melting point is 1,074°C, its boiling point is 1,794°C, and its density is 7.52g.cm
3.
Isotopes
There are 41 known isotopes of samarium. Seven of these are consideredstable. Sm-144 makes up just 3.07% of the natural occurring samarium, Sm-150 makesup 7.38% of natural samarium found on Earth, Sm-152 constitutes 26.75%, and Sm-154 accounts for 22.75%. All the remaining isotopes are radioactive and have very longhalf-lives; therefore, they are considered “stable.” All three contribute to the natural occurrenceof samarium: Sm-147 = 14.99%, Sm-148 = 11.24%, and Sm-149 = 13.82%.
Samarium is one of the few elements with several stable isotopes that occur naturallyon Earth.
Origin of Name
It is named after the mineral samarskite.
Occurrence
Samarium is the 39th most abundant element in the Earth’s crust and the fifth in abundance(6.5 ppm) of all the rare-earths. In 1879 samarium was first identified in the mineralsamarskite [(Y, Ce U, Fe)
3 (Nb, Ta, Ti
5)O
16]. Today, it is mostly produced by the ion-exchangeprocess from monazite sand. Monazite sand contains almost all the rare-earths, 2.8% of whichis samarium. It is also found in the minerals gadolinite, cerite, and samarskite in South Africa,South America, Australia, and the southeastern United States. It can be recovered as a byproductof the fission process in nuclear reactors.
History
Discovered spectroscopically by its sharp absorption
lines in 1879 by Lecoq de Boisbaudran in the mineral
samarskite, named in honor of a Russian mine official, Col.
Samarski. Samarium is found along with other members of
the rare-earth-elements in many minerals, including monazite
and bastnasite, which are commercial sources. The largest
producer of rare-earth minerals is now China, followed by
the U.S., India, and Russia. It occurs in monazite to the extent
of 2.8%. While misch metal containing about 1% of samarium
metal has long been used, samarium has not been isolated in
relatively pure form until recently. Ion-exchange and solvent
extraction techniques have recently simplified separation of
the rare earths from one another; more recently, electrochemical
deposition, using an electrolytic solution of lithium citrate
and a mercury electrode, is said to be a simple, fast, and highly
specific way to separate the rare earths. Samarium metal can
be produced by reducing the oxide with barium or lanthanum.
Samarium has a bright silver luster and is reasonably stable
in air. Three crystal modifications of the metal exist, with
transformations at 734 and 922°C. The metal ignites in air at
about 150°C. Thirty-three isotopes and isomers of samarium
are now recognized. Natural samarium is a mixture of seven
isotopes, three of which are unstable but have long half-lives.
Samarium, along with other rare earths, is used for carbonarc
lighting for the motion picture industry. The sulfide has
excellent high-temperature stability and good thermoelectric
efficiencies up to 1100°C. SmCo5 has been used in making a
new permanent magnet material with the highest resistance
to demagnetization of any known material. It is said to have
an intrinsic coercive force as high as 2200 kA/m. Samarium
oxide has been used in optical glass to absorb the infrared.Samarium is used to dope calcium fluoride crystals for use in
optical masers or lasers. Compounds of the metal act as sensitizers
for phosphors excited in the infrared; the oxide exhibits
catalytic properties in the dehydration and dehydrogenation
of ethyl alcohol. It is used in infrared absorbing glass and as
a neutron absorber in nuclear reactors. The metal is priced
at about $3.50/g (99.9%). Little is known of the toxicity of samarium;
therefore, it should be handled carefully.
Characteristics
Samarium is somewhat resistant to oxidation in air but will form a yellow oxide over time. Itignites at the rather low temperature of 150°C. It is an excellent reducing agent, releases hydrogenwhen immersed in water, and has the capacity to absorb neutrons in nuclear reactors.
Uses
Samarium is easy to magnetize, but very difficult to demagnetize. This makes it ideal forthe manufacture of permanent magnets (SmCo
5) that are part of the hard disks for computers.Samarium is also used as a neutron absorber in nuclear reactors, as well as for lasers andmetallurgical research. It makes up about 1% of the metals in misch metal, an alloy in cigarettelighter flints. It is also one of several rare-earths used in floodlights and carbon-arc lights usedby the motion picture industry. Samarium is used as a catalyst in several industries, includingthe dehydrogenation of ethanol alcohol.
Uses
Arylsulfonyl chlorides and arylsulfinates are reduced by a combination of samarium and titanium(IV) chloride to make diaryl disulfides. It is a neutron absorber, dopant for laser crystals.
Definition
samarium: Symbol Sm. A soft silverymetallic element belonging tothe lanthanoids; a.n. 62; r.a.m.150.35; r.d. 7.52 (20°C); m.p. 1077°C;b.p. 1791°C. It occurs in monaziteand bastnatite. There are seven naturallyoccurring isotopes, all of whichare stable except samarium–147,which is weakly radioactive (half-life2.5 × 10
11 years). The metal is usedin special alloys for making nuclearreactorparts as it is a neutron absorber.Samarium oxide (Sm
2O
3) isused in small quantities in special opticalglasses. The largest use of the elementis in the ferromagnetic alloySmCo
5, which produces permanentmagnets five times stronger than anyother material. The element was discoveredby Fran?ois Lecoq de Boisbaudranin 1879.
Definition
A silvery element
of the lanthanoid series of metals. It
occurs in association with other lanthanoids.
Samarium is used in the metallurgical,
glass, and nuclear industries.
Symbol: Sm; m.p. 1077°C; b.p.
1791°C; r.d. 7.52 (20°C); p.n. 62; r.a.m.
150.36.
Hazard
The salts of samarium are toxic if ingested. These salts react with water, liberating hydrogen,which may explode.
